Heading off aircraft part failures at the pass

Aviation International News » June 2002
October 3, 2007, 12:17 PM

How much would it be worth to be able to reliably predict the structural failure of any part or component of an aircraft long before any flaw becomes visible? To be able to discover that there would be a structural failure in the top of a fuselage, in a vertical stabilizer or even in a landing gear before there was any visible indication such as a crack? Scott Ritchie, director of operations for Boise, Idaho-based Positron Systems, claims his company is offering exactly that technology.

“Our first prototype photon induced positron annihilation [PIPA] technology unit will be available by this fall,” he told AIN. Ritchie anticipates a mobile version of PIPA will be available by year’s end and sell for between $2- and $4 million, depending on a customer’s requirements. The cost would include operator training (technician-level expertise required).

The technology was invented by scientists at the U.S. Department of Energy’s Idaho National Engineering and Environmental Laboratory and licensed to Positron Systems for commercial use. PIPA is a new type of nondestructive testing technology that can precisely detect component fatigue and embrittlement at the atomic level, its proponents claim, and determine remaining useful life. Not only will it help prevent component failure due to fatigue cracks, but it will also safely extend the service life of expensive and critical parts. According to Ritchie, PIPA is more precise than any other existing nondestructive evaluation technology, which includes radiography, eddy current and ultrasonic.

At the smallest scale, defects can consist of a single missing atom, a condition known as a vacancy in the material. At higher defect concentrations, the vacancies may connect into dislocations–the first stage toward what might become a crack. Larger defects with no material in them are called voids. In polymers, which are made up of long molecules, defects may accumulate between molecules and form microscopic holes.

The breakthrough with PIPA is the ability to create positrons within and throughout materials. It has a penetration depth of up to 3.5 in. in materials such as titanium and copper/aluminum alloys, using a one-sided detector process. Penetration depth can be doubled when using a two-sided, two-detector process. Because positrons are being created within the material, PIPA is insensitive to surface conditions such as paint or rust and is largely unaffected by irregularly shaped parts.

The PIPA process involves penetrating materials with a photon beam generated by a linear accelerator. It creates positrons (see box below) that are attracted to nano-sized defects in the material. The positrons collide with electrons, annihilating one another and releasing energy in the form of gamma rays. The gamma ray energy spectrum creates a distinct and readable signature of the size, quantity and type of defects present in the material. What makes PIPA so different is its ability to do this effectively in a wide variety of materials, including metals, composites and polymers. It can also detect a wide variety of fatigue and embrittlement types, such as thermal and mechanical. In doing so, it can quantify the remaining life expectancy of a given material.

Said Steve Bolen, Positron Systems CEO. “Early detection of fatigue and embrittlement damage and identifying the remaining useful life of components will save money, increase safety and extend the uninterrupted operation of critical parts.”

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